BASECOL

• Scientific objectives-

   

  Since the discovery of the first molecule in the interstellar medium (ISM) some fifty years ago, the number of detected molecules has steadily increased with time to more than 200 molecules nowadays (e.g. see the list at www.astrochymist.org/ and www.astro.uni-koeln.de/cdms/molecules). The study of ISM molecules has various motives. First, it has been shown that a relatively rich chemistry can occur in the ISM, where the conditions are rather harsh in terms of temperature and density when compared to those on Earth. This chemistry mainly forms small diatomic molecules but also complex polyatomic molecules, the largest of themorganic,which leads to the unanswered question of what might have been the role of ISM molecules in the terrestrial life appearance. Second, molecules are extremely important for probing the physical conditions of the gas, thanks to the fact that molecular lines are formed under particular temperatures and densities, that depends on the precise molecule structure and observed line.

   

  As a consequence, multifrequency observations can be used to reconstruct the physical structure of the studied object. However, in practice this is only possible if the so-called “collisional rate coefficients” are known. In the vast majority of the conditions present in the ISM, these coefficients are indispensable:

  • to convert an observed signal into a species column density and, therefore, abundance, and
  • to constrain the density and temperature of the emitting or absorbing gas.

  To this end, the molecular dynamics/quantum chemistry communities have been (and still are) extremely active in providing accurate collisional rate coefficients values.

   

  With the advent of a new generation of heterodyne instruments possessing large instantaneous bandwidths, from the ground-based single-dish 30m IRAM [http://www.iram-institute.org/EN/30-meter-telescope.php] to the Atacama Large Millimeter/submillimeter Array [ALMA, http://www.almaobservatory.org/] interferometer, and to the Herschel Space Observatory [http://www.cosmos.esa.int/web/herschel/home], the simultaneous observations of several molecular transitions is routine nowadays. In fact, unbiased spectral surveys are becoming a privileged tool for studying the chemical and physical structure of astrophysical sources.

   

  Finally, the ever-increasing sensitivity of receivers will also lead to an increasing number of molecular lines to interpret. The huge investment in these new observational facilities, makes the knowledge and availability of the collisional coefficients essential. In this context, having easy access to database of collisional coefficients has become more than an urgent need: it is a must.

• Methodology for data-

   

  The primary goal of the BASECOL database is to provide a standard repository of collisional rate coefficients for use by the scientific community. To ensure data quality, inclusion in BASECOL requires the team to critically evaluate any input data by reading the relevant papers and, when necessary, communicating with the original authors. Currently, BASECOL provides collisional data sets as originally published only and archives of earlier datasets for each given collisional system, thus providing long-termpreservation of the data. For guidance to users, BASECOL indicates some sets as “recommended” based on an evaluation by the BASECOL team.

• Services linked to the database-

   

  • New Published Collisional Data can be proposed to BASECOL following instructions at http://basecol.obspm.fr/index.php?page=pages/submitArticles/intro.
  • SPECTCOL: SPECTCOL is a client tool that implements VAMDC [Virtual Atomic and Molecular Data Center, http://www.vamdc.org] standards, retrieve spectroscopic information from CDMS, JPL, HITRAN databases and collisional data from BASECOL. The spectroscopic and collisional information is combined and useful outputs (ascii, xsams, RADEX) are provided for the study of the interstellar medium. In addition the tool allows to scale the collisional rate coefficients and to extract bibliographic information on both spectroscopic and collisional rate coefficients, thus facilitating referencing in publications.

• Contact-

   

  Scientific manager: Marie-Lise Dubernet (marie-lise.dubernet[at]obspm.fr)

  Technical manager: Yaye Awa Ba (yaye-awa.ba[at]obspm.fr)